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Helen Yemm: why astrantias are worth the trouble, stubborn camellias and too-new pots

Flowers of Astrantia major - iStockphoto
Flowers of Astrantia major - iStockphoto

FIGHT FOR YOUR ASTRANTIAS

Am I the only gardener that has trouble growingAstrantia major? My plants survive but don’t thrive, and when I was cutting them down recently I noticed that most of their leaves had ugly brown patches on them that were clearly nothing do with autumn. Is this a disease and should I give up? Belinda Clowes – via email

First, the failure to thrive, which is perhaps about growing conditions: astrantias don’t behave very well if given a hot, sunny place amongst the Border Big Boys. Instead, they tend to appreciate a site in dappled shade with roots in leafy soil that does not dry out.  I find that astrantia’s subtle pincushion flowers also have more impact in slightly shady places, with low-key companions such as ferns, hostas and the leathery summer foliage of hellebores, for example.

The blotchy leaves are almost certainly the evil doings of the larvae of the astrantia leaf miner fly. The fly lays its eggs on the surface of the leaves and the hatchlings burrow into the leaves where they feed and eventually pupate. Two generations are produced during a season (around April and July), and if you are quick off the mark and pinch off any affected leaves you notice early on, you can, as it were, nip the whole problem in the bud. 

The use of a systemic insecticide (Bug Clear Ultra) to control this pest is difficult since astrantias seem to be constantly in flower (thus it is hard to avoid bees). However, I might add also that astrantia is one of those obliging perennials that puts up a brand-new crop of leaves and flowers if cut back severely in August.

This, besides giving us something to admire well into the autumn, also provides a convenient opportunity to “clean up” any blemished plants.  So, to answer your question: No, don’t give up. This is a perennial worth fighting for.

 

Tip for early winter
Tip for early winter

CAMELLIA FLOWER POWER

We have a large camellia bush about 6ft tall and in the 17 years we have lived in this house it has only ever produced one flower bud. Our garden is south-facing, and the soil is quite heavy. What can I do to get it to produce flowers in the coming year?  Jack McLaren – via email

The bad news is that there is nothing you can do at this stage of the year to make your camellia flower next spring. Camellias form their flower buds in the second half of the previous summer. If it has one flower bud now, treasure it (and hope that squirrels don’t pinch it).

There is good news as well as bad, however. There are definitely steps you can take that may make this reluctant beast far more likely to flower in 2019. Next spring, gently loosen the top inch of the heavy soil under its canopy and apply a couple of fistfuls of sulphate of potash and water it in. Afterwards, mulch the ground around the shrub with a generous layer of leaf-mould (if you have it – or buy some ericaceous compost if you haven’t). 

Finally, you mention that your garden is south-facing: it is important that you make sure your camellia is adequately moist round the roots in July and August so, if necessary, water it deeply once or twice, since temporary drought may be at the root of its problem.

HOW TO AGE A POT 

How can I quickly “age” some new terracotta pots so that they fit in with the rest of my nicely weather-worn collection? After a season outdoors they still look brand new and stick out like sore thumbs. Stephanie Wong – via email

You will just have to try to be patient. The problem with new, machine-made terracotta pots is that they have a smooth surface that is less likely, or at least slower, to encourage the natural growth of algae than the older, rougher stuff. 

You will find that if your containers spend this winter outside in the elements, preferably full of compost and standing somewhere shady and damp (rather than empty and stacked up somewhere dry) a very gradual ageing process will have started by next spring.  It might help to smear the outsides of the pots with a thin muddy slurry, which could serve to mask their colour a little as well as attracting the necessary air and waterborne algal spores. 

I discovered another trick quite by chance some years ago: a terracotta pot that had inadvertently found itself submerged in my pond for a month or so turned green with algae the moment it was retrieved from the depths. 

Since then I have always dunked “new” terracotta pots in my pond before planting anything in them.